Lubricating composition containing metal salts of hindered phosphorodithioates



United States Patent of Delaware No Drawing. Filed Apr. 1, 1963,. Ser. No. 269,799

12 Claims. (Cl. 25232.7)

This application is a continuation-in-part of application Serial Number 751,880, filed July 30, 195 8, and now abandoned.

This invention relates to improved lubricating oil compositions which contain metal phosphorodithioates. More particularly this invention relates to improved lubricating oil compositions containing metal phosphorodithioates which are derived from primary alcohols which contain no hydrogen atoms on the beta carbon atom.

The use of the metal salts of dialkylphosphorodithioic acids as oxidation inhibitors in lubricating oil compositions is well known. As such, they are able to increase the useful life of lubricating oil compositions which are susceptible to oxidation. In general, the metal salts of dialkylphosphorodithioic acids have performed well as oxidation inhibitors. Recent trends in automotive design have imposed additional demands on the lubricants used for these engines. The newer engines subject the lubricant to higher temperatures than encountered in the past. It is foreseeable that in the future these temperatures will go even higher. Under these conditions, thermal stability will be a primary consideration in the choice of an oxidation inhibitor.

It is an object of the present invention to provide improved lubricating oil compositions.

It is another object of the present invention to provide lubricating oil compositions having improved thermal stability.

provide lubricating oil compositions containing novel and improved metal phosphorodithioates.

The present invention concerns lubricating oil compositions containing metal salts of phosphorodithioic acids derived from a monosubstituted methanol in which the substituent group is a hydrocarbon radical attached to a tertiary carbon atom. The metal phosphorodithioates, which are present in the lubricating composition, have the following formula:

where R R and R are selected from the group consisting of alkyl, aryl, alkaryl, aralkyl, and cyclic alkyl; M is a metal; and x is the valence of the metal.

The suitable metal phosphorodithioates which are used in this invention have the following formula:

where A is a hydrocarbon radical which can have any of the formulas:

wherein R and R are alkyl groups having from 1 to 5 carbon atoms each, and may be alike or unlike, and R is an alkyl group having from 2 to 18 carbon atoms;

It is still another object of the present invention to 3,21%,275 Patented Oct. 5, 1965 wherein R and R are alkyl groups having from 1 to 18 carbon atoms each, and may be alike or unlike, and R is an aryl group containing from 6 to 10 carbon atoms;

I la

wherein R and R are alkyl groups containing from 1 to 18 carbon atoms each, and may be alike or unlike, and R is an alkaryl group containing from 7 to 20 carbon atoms;

Ru I

R12 wherein R and R are alkyl groups having from 1 to 18 carbon atoms each, and may be alike or unlike, and R is a cyclic alkyl group having from 6 to 12 carbon atoms; M is a metal; and x is the valence of the metal.

The monosubstituted methanols used in the preparation of the novel phosphorodithioates of this invention may also be referred to as primary alcohols having no hydrogen atoms on the beta carbon atom. Examples of suitable materials for use in preparing the phosphorodithioates of this invention include the following:

A. All substituents on the beta carbon atom are alkyl groups 2,2-dimethyl-1-pentanol 2,2-diethyl-l-pentanol 2,2-dimethyl-l-hexanol 2,2-diethyl-1-butanol 2,2,4-trirnethyll-pentanol 2,2-diisobutyll-dodecanol 2,2-diamyl-1-eicosanol 2,2-ditertiarybutyl-l-hexadecanol 2-methyl-2-ethyll-pentanol 2-methyl-2-propyl-l-pentanol 2-ethyl-2-propyl-l -hexanol B. The substituents on the beta carbon atom include aryl groups 2,2-dimethyl-2-phenyl ethanol 2,2-diethyl-2-(p-p'ropy1phenyl) ethanol 2,2-dimethyl-3-phenyll-prop anol C. The substituents on the beta carbon atom include cyclo-alkyl groups 2,2-dimethyl-2-cyclohexyl ethanol 2-cyclohexyl-2-methyll-hexanol 2,2-dicyclohexyll-propanol Of the suitable materials listed above, the materials listed under A, wherein all substituents on the beta carbon atom are alkyl groups, are preferred.

' Metals which may be used to prepare the salts of the phosphorodithioic acids used in my lubricating composition include metals which will give oil-soluble salts and also metals which give oil-dispersible salts. These metals can be any of the following: zinc, barium, magnesium, aluminum, calcium, lithium, lead, tin, copper, cadmium, cobalt, strontium, and nickel. The preferred metal is 21116.

The usual method of preparing phosphorodithioates is by reacting four moles of alcohol with one mole of a sulfide of phosphorus (preferably, phosphorus pentasulfide). The resulting secondary phosphorodithioic acid ester is then converted to the metal salt.

While I do not wish to be bound by any particular theory as to the mechanism of the function of these particular phospohordithioates, when used in my lubricating com-position, I believe the correct explanation is as follows:

Pyrolysis or thermal degradation of esters made from conventional straight-chain primary, secondary, and tertiary alcohols and aliphatic monoand dicarboxylic acids is initiated at the carbonyl oxygen and results in the formation of olefin and acid. This degradation arises from electron migration after formation of an unstable ring structure. To form this intermediate ring there must be hydrogen atoms in the alcohol portion of the ester which are in the sixth atom position from the carbonyl oxygen. These hydrogen atoms must also be coplanar to the carbonyl group or must have rotational freedom if ring formation is to occur. The action is indicated by the following diagram:

(DR-C (50-11(6) (")(1) Original state showing numbering system H H--O Intermediate ring formation 0 R' C H Products after electron I migration Obviously, esters which contain only alkyl or other than hydrogen groups in the six position cannot undergo thermal degradation to yield acids and olefins by this mechanism.

Similarly, by extending this principle, the metal salts of conventional secondary dialkyl phosphorodithioic acid esters were predicted to yield olefins and complex thioacids upon thermal decomposition as illustrated:

Confirmation was obtained by heating a sample of a conventional zinc dialkyl phosphorodithioate at atmospheric pressures. Infrared analysis of the distillate indicated a predominance of olefin.

Alcohols previously disclosed for use in preparing the phosphorodithioates used in prior art lubricating compositions have at least one hydrogen atom on the carbon beta to the hydroxy group. Since the corresponding monovalent metal phosphorodithioates contain two alkyl groups, the number of hydrogen atoms in the six positions, counting from the covalent sulfur atom, are at least two. As all of these hydrogens are subject to thermal elimination, their replacement with alkyl or other non-hydrogen groups will increase the thermal stability of the molecules. Since the number of the six position hydrogen (the six number) in the metal salts may vary quite widely, depending upon the starting alcohol structure, their thermal stabilities will be quite different. Those having the highest six number will be the least stable and those having the lowest, the most stable. It should be noted, however, that only one hydrogen atom is required in this position to allow thermal decomposition. An increased number of these only affects the degree of instability. For illustration, the six number of monovalent metal phosphorodithioates derived from conventionally used commercial alcohols are tabulated below:

Alcohol: Monovalent salt six number n-Hexanol 4 Mixed amyl (Pentasols) *2 2-ethyl-l-hexanol 2 2-ethyl-l-butanol 2 Isooctyl 4 4-methyl-2-pentan0l (methyl amyl) l0 Capryl 10 Isopropyl 12 *Or more.

Commercially, both individual and mixtures of alcohols are used for phosphorodithioate preparations. For example, blends of isopropyl and 4-methyl-2-pentanol are used for economic and solubility reasons. To illustrate further a conventional structure, a graphic formula of the salt derived from the commonly used 4-methyl-2-penta- 1101 is given with the six position hydrogens starred.

The instability of this molecule, when used as a lubricant oxidation inhibitor, is evidenced in internal combustion engines by the formation of excessive piston varnish. This is illustrated under the Caterpillar L-l tests (Example III).

Novel metal salts of phosphorodithioic acids, in which the acid is prepared from completely beta substituted alcohols, e.g., Z-Z-dimethyl-l-pentanol, have no available hydrogen atoms in the six position as described above and are consequently extremely stable thermally. This improvement is reflected in lubricating oil compositions containing hindered metal phosphorodithioates in that the compositions are more stable thermally.

Alcohols having groups other than hydrogen on the beta carbon atom are referred to as hindered. Similarly, phosphorodithioic acids and salts in which there are no available hydrogen atoms in the six position are referred to as hindered.

The lubricating oils which can be used as base oils for my lubricating oil compositions can be any of the oils of lubricating viscosity which are normally used. More specifically, the lubricating oil can be either a mineral oil or a synthetic oil. have a viscosity of about 50 to 2500 seconds, preferably, 75 to 400 seconds, Saybolt Universal at F. The choice of the particular base oil will be determined by the use intended for the lubricant. Since mineral lubricating oils are presently more economical and readily available, they are preferred.

The mineral oil may be a petroleum distillate or residuum oil or mixtures thereof, or may be a synthetic hydrocarbon oil falling within the above-described viscosity range. Also, the oil may be treated in various ways, such as by acid treating, but preferably, is a solvent refined oil.

In general, the oil will I The synthetic lubricating oil can be any of the following:

Alkylene polymers-such as polymers of propylene, butylene, et cetera;

Alkylene oxide-type polymersprepared by polymerizing an alkylene oxide (e.g., propylene oxide) in the presence of water or alcohols;

Carboxylic acid esters-prepared by esterifying a monobasic acid, such as butyric acid, octanoic acid, decan'oic acid, nonanoic acid, 2-ethyl-hexanoic acid, et

cetera, with glycols, such as ethylene glycol, neopentyl glycol, 1,3-propanediol, et cetera; These esters include the so-called complex esters prepared from the aforementioned representative acids and polyhydroxy alcohols.

Dicarboxylic acid esters-prepared by esterifying a dicarboxylic acid, such as adipic acid, azelaic acid, suberic acid, sebacic acid, alkanol succinic acid, fumaric acid, maleic acid, et cetera, with alcohols, such as butyl alcohol, hexyl alcohol, Z-ethylhexyl alcohol, dodecyl alcohol, et cetera;

Liquid esters of acids of phosphorus, alkyl benzenes, polyphenyls (e.g., biphenyls and terphenyls), and alkyl biphenyl ethers;

Polymers of silicon-such as tetraethyl silicate, tetraisopropyl silicates, tetra (4-methyl-2-tetraethyl) silicate, hexyl (4-methyl-2-pentoxy) disiloxane, poly(methyl) siloxane, and poly(methylphenyl) siloxane.

The base oil may contain, in addition to the metal phosphorodithioate, other additives such as detergents, over-based detergents, pour point depressants, anti-foam agents, antioxidants, and viscosity index improvers.

The metal phosphorodithioate content of my lubricating compositions is expressed on the basis of the phosphorus content of the lubricating oil. A suitable amount of metal phosphorodithioate is that amount which contributes a phosphorus content in the lubricating 'oil in the range of about 0.005 to about 0.5 percent by weight. A more suitable amount of metal phosphorodithioate is that amountwhich will contribute a phosphorus content in the lubricating 'oil in the range of about 0.01 to about 0.25 percent by weight. Preferably, the metal phosphorodithioate contributes a phosphorus content in the lubricating oil in the range of 0.04 to 0.10 percent by weight. More preferably, the metal phosphorodithioate contributes a phosphorus content of about 0.065 percent by weight.

In order todisclose the nature of the present invention still more clearly and to more fully illustrate the practical application, the following examples will be given. It is to be understood that the invention is not to be limited to the specific conditions or details set forth in the examples except insofar as such limitations are specified in the appended claims.

EXAMPLE I Apparatus A two-liter, three-necked flask was fitted with a thermometer, stirrer, dropping funnel, Barrett water trap, reflux condenser, and bubble counter.

Procedure To the reaction flask was charged 222.26 grams (1.0 mole) of phosphorus pentasulfide and 500 milliliters of benzene. This slurry was stirred and heated to benzene reflux temperature (81 C.). Dropwise, 500 grams (4.3 moles) of 2,2-dimethyl-1-pentanol was added over 1.2 hours. Hydrogen sulfide was evolved, and after 2 hours at reflux all of the solid was dissolved. After an additional 30 minutes at reflux (95 C.) hydrogen sulfide gas evolution ceased. This mixture was cooled and added from a dropping funnel to a stirred, heated slurry of 93.59 grams (1.15 moles) of zinc oxide in 500 milliliters of benzene contained in the apparatus as above described.

Water (17.8 milliliters) was separated over a six-hour period. Benzene (968 milliliters) was stripped off up to 87 C. at house vacuum. The partially stripped solution was filtered through Filter Cel filter aid to remove excess zinc oxide. The filtrate was stripped by heating to C. at 0.4 millimeter Hg pressure. A yield of 660 grams of syrupy product was obtained. The product was soluble in SAE 30 grade base oil at 0 C. and to a 10 percent by weight level at room temperature (about 18 C.). Also, it was soluble in a detergent consisting of barium -alk-aryl sulmonate overbased with barium carbonate.

Analyses Theory Percent P=8.45 8.65 Percent S=17.74 17.96 Percent Zn=8.71 9.13

EXAMPLE II To provide a sample prepared from an unhindered alcohol, a product was prepared from methyl amyl alcohol in the same manner as described in Example I.

Materials Grams Moles Methyl amyl alcohol 968. 44 8. 5 Phosphorus pentasulfide 444. 52 2. 0 Zinc oxide 179. 03 2.0 Benzene (solvent) 1 1, 500

1 Milliliters.

A yield of 1,250 grams of syrupy product was obtained. It yielded a bright blend at 0.68 weight percent concentration with a detergent consisting of a barium sulfonate overbased with barium carbonate in SAE 30 grade base oil.

Analyses Theory Percent P=9.48 9.47 Percent S=18.5 19.6 Percent Zn=9.8 9.99

EXAMPLE III The product of Examples I and II were incorporated in lubricating oil blends and tested in a Caterpillar engine under CRC L-l conditions. These conditions were as The compositions of the lubricating oil blends were as follows:

Blend A: 4.8 percent detergent (barium alkaryl sulfonate overbased with barium carbonate), 0.77 percent Example I (E0065 percent P), balance SAE 30 mineral oil Blend B: 4.8 percent detergent (same as above), 0.69 percent Example II (0.065 percent P), balance SAE 30 mineral oil The results of the engine tests are shown in the following table:

CATERPILLAR L-l TESTS Blend A Blend B Lacquer rating 49.7 (excellent) O verall rating P 42.8 (unsatisfactory). ass Fail.

*50=perfectly clean.

Thus, it is apparent that a lubricating oil containing a hindered phosphorodithioate is superior to a lubricating oil containing a conventional phosphorodithioate.

While particular embodiments of the invention have where A is a hydrocarbon radical having a formula selected from the group consisting of:

Ra I

wherein R and R are alkyl groups having from 1 to 5 carbon atoms each and R is an alkyl group having from 2 to 18 carbon atoms;

wherein R and R are alkyl groups having from 1 to 18 carbon atoms each, and R is an aryl group containing from 6 to 10 carbon atoms;

wherein R and R are alkyl groups containing from 1 to 18 carbon atoms each, and R is an alkaryl group containing from 7 to 20 carbon atoms;

wherein R and R are alkyl groups having from 1 to 18 carbon atoms each, and R is a cyclic alkyl group having from 6 to 12 carbon atoms; M is a metal selected from the group consisting of zinc, barium, magnesium, aluminum, calcium, lithium, lead, tin, copper, cadmium, cobalt, strontium and nickel; and x is the valence of the metal, said metal phosphorodithioate being present in an amount which will contribute an amount of phosphorus in the range of about 0.005 weight percent to about 0.5 weight percent in the lubricating oil composition.

2. A lubricating oil composition as defined in claim 1 wherein the metal phosphorodithioate has the formula:

wherein R and R are alkyl groups having from 1 to carbon atoms each, and R is an alkyl group having from 2 to 18 carbon atoms; and M and x are as defined in claim 1.

3. A lubricating oil composition as defined in claim 1 wherein the metal phosphorodithioate has the formula:

R4 H i [(R.=. J+O)zPs].M

I ia H wherein R and R are alkyl groups having from 1 to 18 carbon atoms each, and R is an aryl group containing from 6 to 10 carbon atoms; and M and x are as defined in claim 1.

4. A lubricating oil composition as defined in claim 1 wherein the metal phosphorodithioate has the formula:

wherein R and R are alkyl groups containing from 1 to 18 carbon atoms each, and R is an alkaryl group containing from 7 to 20 carbon atoms; and M and x are as defined in claim 1.

5. A lubricating oil composition as defined in claim 1 wherein the metal phosphorodithioate has the formula:

wherein R and R are alkyl groups having from 1 to 18 carbon atoms each, and R is a cyclic alkyl group having from 6 to 12 carbon atoms; and M and x are as defined in claim 1.

6. A lubricating oil composition as defined in claim 2 wherein the metal phosphorodithioate is present in an amount which will contribute an amount of phosphorus in the range of about 0.01 weight percent to about 0.25 weight percent in the lubricating oil composition.

7. A lubricating oil composition as defined in claim 6 wherein the base oil is a mineral lubricating oil.

8. A lubricating oil composition as defined in claim 6 wherein the base oil is a synthetic lubricating oil.

9. A lubricating oil composition as defined in claim 7 wherein the metal phosphorodithioate is a Zinc phosphorodithioate.

10. A lubricating oil composition as defined in claim 8 wherein the metal phosphorodithioate is a zinc phosphorodithioate.

11. A lubricating oil composition comprising a base oil of a lubricating viscosity and a zinc phosphorodithioate having the formula:

said zinc phosphorodithioate being present in an amount which will contribute about 0.065 percent by weight phosphorus to the composition.

12. A lubricating oil composition of claim 11 where the base oil is a mineral lubricating oil having a viscosity of about to 400 seconds, Saybolt Universal at F.

References Cited by the Examiner UNITED STATES PATENTS 2,552,570 5/51 McNab et al. 252-32.7 2,889,354 6/59 Blake et al. 25256 X 2,891,084 6/59 Alm et al 25256 X 3,000,822. 9/61 Higgins et al. 2523.7

OTHER REFERENCES Barnes et al., Synthetic Ester Lubricants, Lubrication Engineering (August 1957), page 454 pertinent.

DANIEL E. WYMAN, Primary Examiner.- 

1. A LUBRICATING OIL COMPOSITION COMPRISING A BASE OIL OF LUBRICATING VISCOSITY AND A METAL PHOSPHORODITHIOATE HAVING THE FORMULA: 